Smallpox: the disease that changed empires

For more than three thousand years, smallpox was one of the most feared diseases on the planet. It respected no borders and no social class: it killed pharaohs, emperors and peasants alike, left millions of survivors blind and permanently scarred, and, on more than one occasion, decided the fate of entire civilizations. In the twentieth century alone it is estimated to have caused around 300 million deaths. And yet it is the only human disease that medicine has managed to erase completely from the face of the Earth.

An ancient disease

Smallpox was caused by the variola virus, and its trail is extremely old. The best-preserved pustules we know of appear on the mummified skin of pharaoh Ramesses V, who died around 1145 BC. From there it traveled the ancient world along trade and military routes: there are descriptions consistent with the disease in Han-dynasty China, in India, in the Roman Empire —the so-called Antonine Plague of the second century may have been related— and in medieval Europe.

The symptoms were horrific: high fever, followed by an eruption of pustules that covered the body, including the face, the palms and the soles of the feet. In its most severe forms it killed about a third of those infected; those who survived were usually left with deep scars and, frequently, blindness. It was such a constant companion of human life that many cultures treated it almost as an inevitable rite of passage of childhood.

The unwitting weapon that toppled empires

The most dramatic chapter in the history of smallpox happened on the other side of the Atlantic. When Europeans reached the Americas in the early sixteenth century, they brought with them a virus against which the Indigenous peoples had no immune defense: they had never been exposed to it.

In 1520, during Hernán Cortés's campaign, smallpox reached Tenochtitlan, the Aztec capital. In a single year the epidemic is estimated to have killed a huge share of the city's population —some estimates cite up to 40 percent— and beheaded its leadership at the worst possible moment. A handful of Spaniards could not have subdued a city of hundreds of thousands; the virus did much of the work. Cortés took the capital in 1521.

Something similar happened farther south. Smallpox outran the conquistadors themselves and reached the Inca Empire around the mid-1520s, before Francisco Pizarro set foot in the Andes. The disease killed the emperor Huayna Capac and his heir, unleashing a civil war between his sons Huáscar and Atahualpa that left the empire divided and exhausted just as the Spanish arrived. To a large extent, smallpox rewrote the map of the continent. It is no accident that imported diseases are often described as the real engine of the conquest, a phenomenon that also appears when you study how Europe learned to isolate the sick with quarantine.

The first attempts at defense

Long before a vaccine existed, different cultures independently discovered a bold idea: deliberately exposing a healthy person to a mild form of the disease to protect them from a severe one. This was variolation. In China it had been practiced for centuries by blowing ground smallpox scabs into the nose; in India and the Ottoman world, material from a pustule was inoculated under the skin.

It was in Constantinople that an English aristocrat, Lady Mary Wortley Montagu, wife of the British ambassador, saw the method in action around 1717. She had herself survived smallpox, which had ruined her face and killed a brother. Convinced, she had her own children inoculated and, on returning to London, championed the technique in Britain around 1721, in the middle of an epidemic. Variolation often worked, but it was risky: a small percentage of those inoculated fell gravely ill or died from the "treatment" itself.

The decisive leap came in 1796, when the country doctor Edward Jenner showed that inoculating the harmless cowpox protected against the human disease, with almost no risk. From that discovery came the word "vaccine" —a story that deserves its own chapter, which we tell in the origin of the word "vaccine"—. For the first time, humanity had a real weapon against its old enemy.

The only human disease ever eradicated

Having the vaccine was not enough: it had to be carried, dose by dose, to the last corner of the world. In 1967 the World Health Organization launched an intensified global eradication program. Instead of trying to vaccinate everyone, the key strategy was surveillance and containment: detect every outbreak and vaccinate in a ring around all contacts to break the chain of transmission.

It worked. The last natural case of the most severe variant was recorded in 1975, and the last natural case of smallpox in the world was that of Ali Maow Maalin, a hospital cook in Somalia, diagnosed in October 1977. He survived, and none of his many contacts caught the disease. After two years of searching without finding a single new case, the WHO officially declared the eradication of smallpox in 1980. It was —and remains— the first and only human disease completely eliminated thanks to vaccination.

The history of medicine is full of these long, surprising battles, such as the bark that became both a malaria remedy and gin and tonic. But few end so well. Today the variola virus exists only, frozen, in two maximum-security laboratories, one in the United States and one in Russia. A disease that for millennia changed the course of empires ended up reduced to two guarded freezers: perhaps the greatest triumph of public health in history.

References

1. «Smallpox», World Health Organization (WHO). who.int
2. «History of Smallpox», Centers for Disease Control and Prevention (CDC). cdc.gov
3. «Smallpox», Encyclopædia Britannica. britannica.com
4. «Ali Maow Maalin», Wikipedia. en.wikipedia.org

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